EuroWattCalc
Tariff tool

Time-of-use shift calculator

Estimate what it is worth to run an appliance at an off-peak rate instead of a peak rate, using the two prices printed on your own tariff.

Reviewed 2 September 2026Calculations run locally in your browser

Peak vs off-peak

Enter one appliance or one repeated load, then the share of it you could realistically move.

Monthly energy—kWh — unchanged by shifting
All at peak rate—per month
After the shift—per month
Monthly difference——

This compares two rates applied to the same consumption. Standing charges, taxes and any difference in contract terms are excluded.

The formula behind the result

Energy per cycle: watts ÷ 1,000 × hours per cycle
Monthly kWh: energy per cycle × cycles per month
Cost at peak only: monthly kWh × peak rate
Cost after shifting: (monthly kWh × (1 − share)) × peak rate + (monthly kWh × share) × off-peak rate
Monthly difference: cost at peak only − cost after shifting

The annual figure is simply the monthly difference multiplied by twelve, which assumes the same usage pattern every month. Seasonal loads such as heating or air conditioning will not follow that assumption.

Choosing a realistic share

The share moved off-peak is the input people overestimate most. A dishwasher with a delay timer can plausibly run 80–100% of its cycles overnight. A washing machine drops lower if you need clothes the same evening, and cooking rarely moves at all.

A useful test: if running the appliance off-peak requires you to change your schedule rather than the appliance's schedule, the realistic share is lower than you think. Set it deliberately low and see whether the saving still justifies the effort.

Loads that usually shift well

  • Dishwashers and washing machines — most have a delay-start function, and the cycle does not need supervision.
  • Electric vehicle charging — often the single largest shiftable load in a household, and most EVs and wallboxes support scheduled charging. The EV charging calculator covers this case in more detail.
  • Hot water cylinders — an immersion heater on a timer stores heat overnight for use the next day.
  • Tumble dryers — shiftable when a load can simply wait until morning.

Loads that usually do not

  • Cooking — tied to meal times, not to tariff windows.
  • Lighting and electronics — used when the household is awake, which normally overlaps the peak window.
  • Refrigeration — runs continuously across both rate periods and cannot be scheduled.
  • Space heating — shiftable only with thermal storage; otherwise it is needed when it is needed.

Before switching to a time-of-use tariff

Model the shift on your existing consumption first. A time-of-use tariff is only better if the amount you genuinely move off-peak outweighs the higher price you pay for everything left at peak. Run this tool once with an optimistic share and once with a pessimistic one — if the pessimistic case is not clearly positive, the switch is marginal.

Also check whether the tariff requires a smart meter, whether the off-peak window is long enough for your appliances to complete a cycle, and whether the rates are fixed for the contract term. These practical constraints decide more outcomes than the arithmetic does.

Next steps

To find which appliances are worth shifting in the first place, build a whole-home energy budget and look at the largest contributors. If an appliance is a big driver but cannot be shifted, test replacing it with the upgrade payback calculator.

Frequently asked questions

What is a time-of-use electricity tariff?

It is a tariff that charges different prices per kWh depending on the time of day. A peak rate applies during high-demand hours and a lower off-peak rate applies at other times, usually overnight.

Which appliances are easiest to shift to off-peak hours?

Loads with a delay timer and no need for supervision are the easiest, such as dishwashers, washing machines, water heaters and electric vehicle charging. Cooking, lighting and heating are usually tied to when you are actually at home.

Does shifting usage reduce the total kWh I consume?

No. Shifting changes the price paid per kWh, not the amount of energy used. The total consumption stays the same and only the rate applied to part of it changes.

Why might my saving be smaller than this calculator shows?

Time-of-use tariffs often carry a higher standing charge or a higher peak rate than a flat tariff. This tool compares rates on the same consumption, so it does not capture a change of contract or any fixed charges.

Where do I find my peak and off-peak rates?

Both rates are printed on the electricity bill or in the contract summary, usually alongside the hours during which each applies. Meter readings may also be split into separate registers for each rate.